I am trying to understand the nature of infections in beer. I find it difficult to imagine ( considering there are wild yeasts and moulds and micro-organisms in the air - aren't there? ) a scenario where a beer is 100% free of infection, or is this normally the case with a properly brewed batch? Or is it a case that when infection is lower than some threshold we don't notice it and that beer is considered to not be infected?

I am interested because being new to homebrew and educating my palate, particularly with regard to off flavours I often wonder whether I have some kind of infection. But I would usually discount this if the beer is question is pretty drinkable, because I would have assumed that an infected beer would REALLY stand out and not really the kind of thing easily confused with an off flavour, but considering what I was asking about above; could it be possible to have a small amount, or even a tiny amount, of infection being responsible for off flavour if we define infection as "above a certain ( detectable ) threshold"?

If that's the case then is it a case that we're trying to reduce infection rather than avoid it, or is it possible to avoid it altogether - and is it a case that minute infections are common but to the degree that we eradicate these we are likely to get better tasting beers?


First, technically all beer is infected, since you pitch yeast. To be pedantic, what you're talking about is contamination. And yes, I'd say pretty much all homebrew (and even commercial beer) is contaminated to some extent. The type and severity of the contamination can vary, however.

  • So with the exception of sours or something do lower levels of contamination always improve the taste. I mean if all beer is contaminated to some extent then does it follow then that the better beers ( sought after / competition winning etc ) would generally have to have little or no contamination to be highly regarded. I'm asking because I'm always wondering whether it's that I'm too obsessive ... or whether I'm not obsessive enough ... about sanitation. Is it a case of a law of diminishing returns or is it actually an achievable goal to have virtually zero contamination :-) Feb 28 '17 at 21:57
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    Intentionally pitched microbes (yeast) wouldn't really qualify as it being infected, pedantic-ness aside.
    – brewchez
    Mar 1 '17 at 11:27
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    @byronasgur - Yes, the best beers will have the least contamination. Most bacteria/wild yeasts will make some contribution to flavor, and even though low-levels may be barely perceptible. they may be enough to make your beer less enjoyable than a less contaminated beer. This is why you need to pitch an adequate quantity of active yeast cells -- it is a race to see which microbes will consume the most sugar. When the yeast multiplies quickly enough, it crowds out and starves the invaders
    – jalynn2
    Mar 1 '17 at 18:43

YES. All biological contaminations (infections) take time to do thier thing. So yes there are levels to an infection. Acetobactor for example, can be at a range of non detectable to the palet to full on vinegar.

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